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Homework Help: E=mc^2 homework problem

  1. Jan 14, 2010 #1
    1. The problem statement, all variables and given/known data
    A tritium nucleus is formed by combining two
    neutrons and a proton. The mass of this nucleus
    is 9.106 × 10–3 universal mass unit less than the
    combined mass of the particles from which it is
    formed. Approximately how much energy is
    released when this nucleus is formed?
    (1) 8.48 × 10–2 MeV (3) 8.48 MeV
    (2) 2.73 MeV (4) 273 MeV


    2. Relevant equations

    E=mc^2

    3. The attempt at a solution
    I tried finding the energy by using what they gave me(9.106 × 10^-3) and fixing into the equation E=mc^2, but my anwser turns out 8.2 × 10^13( which obviously missing something)
     
  2. jcsd
  3. Jan 14, 2010 #2

    sylas

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    Re: E=mc^2

    Think about what units you are using. You may need to convert units.
     
  4. Jan 14, 2010 #3

    vela

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    Re: E=mc^2

    You can't just plug the numbers you have in and get the right answer because the units don't work out.
     
  5. Jan 14, 2010 #4
    Re: E=mc^2

    so how do I change form Joules to Mega Electron Volts? do I multiply or divide by 1.6 *10^-19... that is where I tend to get confused.
     
  6. Jan 14, 2010 #5

    Matterwave

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    Re: E=mc^2

    Is a joule larger or smaller than a MeV?

    So if I have 1 joule, should have 1*1.6*10^-13 MeV or 1/(1.6*10^-13) MeV? Which one gives a bigger answer?

    Also, for mega electron volts the conversion factor is 1.6*10^-13 not -19, -19 is for electron volts.
     
  7. Jan 15, 2010 #6

    sylas

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    Re: E=mc^2

    You also need the mass units to be right.
     
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